Why aren't there super large predators in the sea anymore? by Ewald Groenewald
Answer by Ewald Groenewald:
There are, and they are the largest, most fearsome predators to ever exist.
The largest animal to ever exist (which biologist know of) is the blue whale. Although it’s not technically a predator, the blue whale is a, which makes it a filter feeder, and feeds on living organisms like krill (euphausiids) and copepods.
However, the largest strictly predatory animal that has ever existed is the sperm whale. It is a toothed whale and hunts squid, and sometimes it hunts the colossal squid, another massive predator.
There are some pretty amazingon the internet of battles between sperm whales and giant squids, all speculatory of course, seeing as sperm whales hunt at extreme depths and the whole battle is somewhat mysterious.
However, evidence suggests that the battle is quite fierce, considering the squid’s anatomy. They have massive hooks on their arms and tentacles, that tear and hook into flesh. The evidence is quite clear when looking at the sperm whale’s skin.
Left (a) are the serrated suckers of the, and right (b) are the hooks of the .
Edit 1: Aspoints out, the colossal squid might not be as large as depicted in the image below. However, the question marks indicates the lack of information.
Colossal squids are very elusive, as they live at extreme depth and cold, and there are very little specimens available for study. Specimens have been collected by sheer luck, either by fishermen who accidentally catches them, or from the stomach contents of hunted sperm whales. In 2005 the first footage of a live specimen was captured by a group of Japanese biologists. The first specimen, and the discovery of the species only occured in 1925. Since then very few complete specimens have been studied. The second fully intact specimen was only captured in 2014, and it measured in at 3.5 m.
The largest complete specimen is about 5.4 meters long, much smaller than usually presented or estimated.
Biologists estimate the massive size of the colossal squid based on the polysaccharide (chitin) beak, which takes a long time to digest, which have been found in the stomachs of sperm whales. The sizes of these beaks are indicative of the size of the animal, and some suggest that the size of some of these squid must reach at least 10 m.
They also base the estimated size of the colossal squid relative to the giant squid, and the comparative damage they do to sperm whales.
The giant squid has many more specimens available for study and its size has been readily documented as can be seen in the image below (image below the truck comparison), which was compiled by the National Evolutionary Synthesis Centre (sizes based on actual specimens collected).
From this biologists can infer that if the giant squid does minimal damage with its serrated suckers, and it can reach massive sizes, then the massive damage done by the hooks of the colossal squid must indicate that they too must reach these massive sizes, if not larger.